This invention relates to the control of multiple oxidizer levels in water treatment processes, and particularly relates to the use of a combination of sensors including at least one amperometric sensor isolated by a gas permeable membrane.
In the areas of both pool water and waste water treatment, there has been an increased trend toward combining oxidizers to achieve a synergistic effect, thereby exceeding the performance of the individual oxidizers. Although there is no question as to the benefits provided by the use of synergistic oxidizer chemistry, the ability to control their concentrations, ratios, and optimize their feed rate in real world applications has proven to be a difficult task. This often leads to overfeeding to ensure adequate results.
Most oxidizer feed applications incorporate either ORP (Oxidation Reduction Potential) or wet chemistry methods which use color change reagents,. e.g. DPD, to indicate the presence and concentration of the oxidizer. ORP has become increasing popular due to its ability to control the feed of oxidizer based on the oxidizer demand.
In many water treatment applications the demand for oxidizer can change over time. In pools for example, as bathers enter the pool water, organic contaminants are introduced to the water that impose a demand on the oxidizer (usually chlorine). In order to maintain the same oxidation potential, the ORP controller would increase the concentration of chlorine in the water. This process ensures enough oxidizer has been added to not only satisfy the organic demand, but also to ensure sufficient residual oxidizer is available to effectively sanitize the water.
In the pool example, chlorine is the sanitizer and therefore must be maintained in sufficient concentrations to effectively provide for a safe bathing environment. However, if another oxidizer is added to the pool water to enhance oxidation of organic contaminants, the ORP based control system can be compromised since either chlorine or the second oxidizer can satisfy the ORP setting.
Should chlorine feed be compromised, the second oxidizer could be fed in sufficient concentrations to meet the ORP set-point. In this instance, sanitation of the water could be compromised. Also, because chlorine concentrations are reduced, the synergistic effects provided by the combined effect of the two oxidizers would also be compromised.
U.S. Pat. No. 5,239,257 to Muller et al teaches an amperometric probe with a gas permeable membrane. The patent fails to teach or disclose a measuring system for controlling oxidizers in a water treatment process by combining multiple sensors inclusive of at least one gas permeable membrane enclosed amperometric sensor.
U.S. Pat. No. 5,902,751 to Godec et al teaches a method for the measurement of dissolved carbon employing a gas permeable membrane dividing deionized water from the oxidized sample water and a pair of micro-conductivity and temperature sensors.
U.S. Pat. No. 6,030,842 to Peachey-Stoner teaches a method for determining free halogens in aqueous fluids utilizing an azine indicator material and a benzidine type catalyst material impregnated into a matrix carrier.
The prior art fails to teach or suggest a system for determining and controlling the amounts of free oxidizer in a multiple oxidizer system.
Many water treatment applications incorporate two oxidizers that together provide a synergistic effect. For example, Advanced Oxidation Technologies (AOTs) can employ ozone with peroxide to produce hydroxyl free radicals (hydroxyl radicals). In yet another similar application, hydrogen peroxide is converted to hydroxyl free radicals using ultra violet radiation. While one oxidizer is predominant, the production of hydroxyl radicals makes for a two-oxidizer application. There are other similar processes used in AOTs with the results being to produce hydroxyl free radicals.
In yet another water treatment application, a halogen based oxidizer such as chlorine is used in combination with peroxygen based oxidizers such as potassium monopersulfate to effectively eliminate the formation of volatile halogenated nitrogen based compounds into the air of indoor aquatic facilities. In this application, both chlorine and monopersulfate are fed to the pool water based on ORP based control.
Although these applications take advantage of the synergistic properties which flow from the use of two oxidizers, they nevertheless fail to optimize the control and/or optimize the feed or production of each oxidizer based, on program performance, e.g. oxidizer demand.
For example in the pool, while ORP initiates oxidizer feed based on demand for the oxidizer(s), this method of control does not clearly differentiate between the oxidizers. Oxidizers are fed proportional to one another. Using this control scheme, dynamic optimization of oxidizer ratios, and verification of individual oxidizer feed is not possible. Similar inefficiencies exist with AOTs.
Accordingly, it is an objective of the instant invention to teach a method of operation and apparatus for performing the method which combines the use of either ORP or amperometric sensor technology, along with at least one amperometric sensor that employs a gas permeable membrane to provide superior process control in two oxidizer systems. The gas permeable membrane described in this application will have the ability to allow gases and/or nonionic compounds to permeate while restricting ionic particles from permeating.
It is a further objective of the instant invention to teach a process wherein the combination of sensor technologies can, in many two oxidizer applications, independently control the oxidizers, verify concentration or presence of both oxidizers, and enhance the optimization of oxidizer(s) feed rates in dynamic systems.
Other objectives and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. The drawings constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof.